The invention relates to a circuit arrangement for every economy in a drive which includes an induction motor and a clutch-brake unit. Windings of the induction motor are dimensioned so that its speed is virtually constant in a stable range under normal service conditions. The clutch-brake controls output speed.
Energy economy circuits for motors have attained interest particularly for mobile appliances which are fed from limited energy accumulators. This is particularly of interest in view of the so-called energy crisis. A circuit arrangement is known from German Offenlegungsschrift No. 27 30 774, in which the energy consumption of an alternating-current induction motor is minimized under different service conditions by determining the loss factor (cos. .rho.) on the basis of current and voltage measurements at the motor and maintaining its constant using electronic circuitry at the level which it assumes at nominal speed and nominal load. This results in a reduction in the stable speed and torque range, so that such a circuit arrangement has only limited usefulness.
A motor circuit for energy economy is known from German Offenlegungsschrift No. 28 24 474, in which the speed of the motor is maintained constant irrespectively of the load. A separate speed detection device is necessary for this purpose. When alternating-current induction motors are used in the field of sewing machines, in which the output speed is controlled by clutch brake units, the known energy economy circuits are unsuitable from the standpoints both of outlay and of use. This is because, by the use of suitable alternating-current induction motors, the speed thereof remains virtually stable in any case if such motors are kept in the stable speed range.